1. Field of the Invention
The present invention relates to an optical device, and more particularly to a structure for optically coupling the light emitting section of a light-emitting device with an optical waveguide.
2. Description of the Related Art
As the speed of communication systems is getting faster and their band is becoming broader, the amount of signal processing in a signal processor is increasing tremendously. Particularly, optical means is required for fast transfer of the vast amount of information between modules in a transmission apparatus. These days, such a huge amount of information processing is accomplished generally by a parallel optical interface module which transmits and receives a plurality of light signals in parallel.
Laser diodes are used as typical light emitting devices on the transmission side of a parallel optical interface module, with a plurality of optical fibers arranged in association with their light emitting areas. It is necessary to align the optical axes of those optical fibers with the light emitting region at a high precision (for example, a precision of less than 5 xcexcm).
There have been known two types of laser diode: an edge-emitting laser diode and a surface-emitting laser diode. In the case of the edge-emitting laser diode, since the pass/fail check cannot be performed before those devices are cut out, the increasing number of light emitting sections to be formed on a single device reduces the production yield. The edge-emitting laser diode is therefore disadvantageous in its use in a parallel optical interface module. Another disadvantage is that the light emitting sections can be formed only linearly, resulting in the limited number of parallel transfers.
By way of contrast, in the case of surface-emitting laser diodes, the pass/fail check can be performed in such a state that those laser diodes are formed on a semiconductor wafer, resulting in a higher production yield. Further, the light emitting sections can be arrayed two-dimensionally, so that the surface-emitting laser diode is advantageous over the edge emitting type in the number of parallel transfers. However, a consideration should be made on how to couple the two-dimensional array of light emitting sections to optical fibers. If the edges of optical fibers are laid perpendicular to the two-dimensional array of light emitting sections, the device undesirably becomes large besides the difficulty of holding multiple optical fibers in the perpendicular direction.
In Japanese Unexamined Patent Publication No. 2-234476, disclosed a structure in which a mirror surface inclined by 45 degrees is formed on each light emitting region of a surface-emitting laser diode to allow lights from the two-dimensional array of light emitting sections to travel in parallel to the light emitting surfaces and enter the optical fibers.
In Japanese Unexamined Patent Publication No. 4-308804, disclosed an optical module in which reflective surfaces formed by obliquely polishing the ends of optical fibers are provided on a light emitting/receiving device and lights are input to and output from the light emitting surfaces in parallel to the light emitting surfaces.
The method which forms inclined mirror surfaces on the light emitting surfaces of each surface-emitting laser diode for optical coupling to the associated optical fibers requires a step of separately forming the reflective surfaces and optical fibers and further requires the space where the mirror surfaces are provided.
The method which cuts optical fibers and forms reflective surfaces on their edges also requires a step of separately forming the reflective surfaces and optical fibers. This method may be effective for linearly arranged light emitting sections. When the light emitting sections are arrayed two-dimensionally as in the case of surface-emitting laser diodes, however, it is necessary to cut each optical fiber at different lengths and to polish each cut fiber. This not only complicates the production process, but also makes the positioning of the optical fibers significantly difficult.
Accordingly, it is an object of the present invention to provide a structure capable of optically coupling a light emitting device and an optical waveguide easily and accurately.
It is another object of the present invention to provide a compact optical device which has a light emitting device and an optical waveguide optically coupled together and is easy to manufacture.
According to one aspect of this invention, there is provided an optical coupling structure for optically coupling a light emitting device to an optical waveguide having a center portion of a relatively high refractive index and a peripheral portion of a relatively low refractive index, which structure comprises a V-shaped inclined portion provided on part of the optical waveguide; and a light-incident section formed on a protruding side of the V-shaped inclined portion in association with a light emitting section of the light emitting device.
The optical coupling structure may be formed by bending a predetermined portion of the optical waveguide into a V shape, yielding a V-bent portion; and forming a light-incident surface on a protruding portion of the V-bent portion. It is preferable to fix both sides of the predetermined portion of the optical waveguide, and to move at least one of the both sides by a given distance in an optical waveguiding direction of the fixed optical waveguide toward the predetermined portion, thereby forming the V-bent portion at the predetermined portion.
As part of an optical waveguide like an optical fiber is used to form a V-shaped inclined portion and a light-incident section, the optical waveguide can be arranged in parallel to the surface where the light emitting sections of a light emitting device are formed. This can decrease the required space considerably.
Further, the V-shaped inclined portion at part of the optical waveguide can be formed by positioning that part with respect to the light emitting section of the light emitting device, so that optical coupling can be realized merely by high-precision two-dimensional positioning. For example, a surface emitting light emitting device having a plurality of light emitting sections arrayed two-dimensionally can be coupled to a plurality of optical waveguides just by two-dimensional positioning, and the production of the optical coupling structure becomes significantly easier.
As the flux of rays from a light emitting section is split into two by the V-shaped inclined portion, the split lights can be used for different purposes. This structure is extremely advantageous in the field of application. For example, one output light can be used for data transfer while the other can be used for monitoring a light emitting device. Alternatively, one output light can be used for data transfer for an operating system while the other can be used for data transfer for a reserved system.